A number of movable parts in a wind turbine need to be locked in certain conditions. For example, the generator rotor in a wind turbine generator must be locked against rotation relative to the generator stator or to the nacelle for maintenance and/or repair operations.
According to current applicable guidelines for the certification of wind energy plants, provision must be made for the positive locking of the rotor. Therefore mechanical interlocking should be provided in the wind turbine for performing the above mentioned operations and in general for purposes where the rotor must be locked against rotation. This means that for example frictional brakes and the like are not allowed according to these guidelines.
In this respect, it is known in the art the use of locking arrangements for locking the rotor of a wind turbine generator against rotation. These locking arrangements comprise one or more locking pins that are fixedly arranged to the stator of the wind turbine generator. When service activities are required in the wind turbine, a brake assembly is actuated to stop the wind turbine in operation. Once the wind turbine generator is stopped, the locking arrangement can be then activated to lock the rotor against rotation. The activation of the locking arrangement is carried out by driving a locking member or locking pin into a corresponding locking housing that is usually formed in the rotor. Driving of the locking pin can be carried out manually or hydraulically along the axis of the locking pin. The axis of the locking pin is substantially parallel to the rotor axis. Once the locking pin is inserted into a target locking hole, the rotor is prevented from being rotated relative to the stator and service activities can take place safely.
One of the major drawbacks associated with the locking of mutually rotating elements in a wind turbine, such as the rotor relative to the stator, according to the above known method, is the large tolerances existing in the relative position of the locking pins and the locking holes when in the locking position. This further results in alignment problems of the locking pins and the corresponding locking holes.
Another problem with known locking arrangements is that wind turbines are currently becoming bigger in order to produce more energy. This involves increased dimensions of the generator such that the locking pins are also bigger. Since the locking pins must be manufactured to withstand the requirements of operating within harsh working conditions of the wind turbine, costs become undesirably high. This also applies to the actuating mechanisms for driving the locking pins into and out of the locking position which need to be dimensioned in order to withstand high loads. This again results in high costs and overweight.
In addition, the increased dimensions of the wind turbines and parts thereof have led to increased loads on the locking arrangement. Consequently, concentration of shear forces has become an important issue. Alternative materials for the locking arrangements or the increase in their size are solutions that are not useful for withstand the extremely high loads involved in current wind turbines.
Although the use of several locking pins could help to solve this problem, costs and misaligning problems still remain.
Document EP1291521 discloses a locking arrangement for a wind turbine rotor. The locking arrangement in this case comprises an axially movable locking pin that is arranged on the nacelle structure and corresponding locking housings formed in the wind turbine rotor. The locking pin has a tapered end for compensating for misalignments and plays into the holes. Due to the location and the small dimensions of the working plane of the locking pin where shear forces are concentrated, extremely high stresses are present resulting in a highly potential risk of failure of the locking pin when the locking arrangement is in a locking position.
Document WO2008059088 discloses an adjustable, self-aligning rotor locking device for preventing the hub from being rotated relative to the wind turbine nacelle. The rotor locking device includes locking pins fixed to the nacelle and actuation means for driving the locking pin axially in relation to at least one corresponding hole formed in the hub. In this case, the location and the small dimensions of the working plane of the locking pin where shear forces are concentrated is the same as the above document such that extremely high stresses are present with a resulting potential risk of failure of the locking pin.
Many other locking arrangements have been provided having in common the location and the small dimensions of the working plane of the locking pin where shear forces are concentrated. For example, documents WO2010102967, WO2005090780 and WO2008155053 all describe locking arrangements for wind turbine applications where a locking pin is movable in a direction towards a locking housing for locking the parts against rotation.
Due to the fact that the locking pin is subjected to high loads when in the locking position and that said loads are concentrated on a small working plane of the locking pin, loads concentrated therein result in that the locking pin may be likely to deform, crack or break when in the locking position. In addition, it also remains difficult to compensate for radial misalignments in prior art locking arrangements.